This invention relates to magnetic disk storage units of movable head type, and particularly to a magnetic disk storage unit having a function for removing dust deposited on the magnetic disk surface and magnetic head when the unit starts to operate or is continuously operating.
The construction of a magnetic disk storage unit is shown in FIG. 1. A magnetic disk 3 for storing information thereon is fastened to a hub 4 of a spindle motor 5. A magnetic head 7 for reading information from or writing it in the magnetic disk 3 is mounted on a carriage 8 which is moved by a screw 10 of pulse motor 9 in the direction of an arrow 13. The magnetic head 7 is in contact with the surface of the magnetic disk 3 when the magnetic disk 3 is stationary, but is floated away from the surface of the magnetic disk 3 when the magnetic disk 3 starts to rotate and increases the revolution rate, that is the so-called contact start-stop (hereinafter, abbreviated CSS) system is employed. The CSS system needs no control mechanism for loading and unloading of the magnetic head to and from the magnetic disk surface, and therefore at present it is used in most of the magnetic disk storage units. FIG. 2 is a graph showing the situation in which the magnetic disk 3 rotates. In FIG. 2, the ordinate indicates the revolution rate of the magnetic disk 3, and the abscissa the time. The magnetic disk 3 is driven to rotate from a start point O and reaches a steady state of rotation, A as illustrated. The magnetic head 7 is at first not floated away from the magnetic disk surface due to the rough surface of the magnetic disk 3 and the pressing force of a plate spring 20 of the magnetic head 7 against the disk surface until the disk 3 reaches a peripheral speed of 10 m/sec. After it reaches that speed, the head 7 is floated away from the disk surface, and at the steady state of rotation, or peripheral speed of disk 40 m/sec, the head 7 is floated by 0.5 .mu.m away from the disk surface. To stop the magnetic disk 3 from rotation, the power switch for the spindle motor 5 is turned off and a brake 6 provided is operated to stop the disk in a short time as shown by straight line B--C. If the brake 6 were not provided, the disk 3, after turning off the power switch, would follow a curve B--D as shown, so that the head 7 slides on the disk 3 for a long time.
The magnetic head 7 is aerodynamically floated by a small amount of gap above the magnetic disk 3, and the gap becomes smaller and smaller as the memory capacity increases. When the gap is in the order of sub-microns, even the dust particles in suspension in air become a problem. Thus, in order to prevent unclean air in the exterior, 18 of a disk chamber 17 from entering into the disk chamber 17, a packing 19 is used to provide a seal between the base 1 and the cover 2. The parts to be incorporated in the disk chamber 17 are rinsed and assembled in a clean room in which the amount of dust is reduced. The dust particles are flown up by CSS and are carried on an air flow 12 caused by the rotating force of the magnetic disk 3 and removed through a dust filter 11 provided at the center of the disk 3.
In such a magnetic disk storage unit, the flown up dust particles, when the magnetic disk 3 starts to rotate in sliding contact with the head 7, are floated in air, carried on the air flow 12 and collected by the dust filter 11. The air flow 12, however, is reduced in its flow rate in the period of slowing down of the disk 3 so that the dust particles are not collected by the dust filter 11, but drift in air and soon are deposited on the surface of the magnetic disk 3. FIG. 4 shows the dust particle 14 deposited on the disk surface relative to the magnetic head 7. As shown in FIG. 4, when the disk 3 starts to rotate, the magnetic head 7 is located at a position indicated by a broken line, and when the disk is in the steady state of rotation, the head 7 at a position indicated by a solid line. When the disk 3 starts to rotate, and when the dust particle 14 deposited on the disk surface is at a position where it collides with the head 7, the dust particle 14 is removed by the rotation of the disk 3. However, since the dust particle 14 is usually distributed on the entire surface of the disk 3 and therefor some dust particles are left thereon, the head 7 will often collide with the dust particle 14 when the disk 3 reaches the steady state of rotation.
Moreover, when the magnetic disk storage unit is operated continuously (in some case, for several years), the dust particles within the sealed chamber are deposited on the head to narrow the spacing between the head and the disk, and finally the head may collide with the disk.
On the other hand, the energy generated when the disk 3 is made to be in sliding contact with the head 7 is proportional to the square of the speed of the disk, as shown in FIG. 3, in which the ordinate represents the sliding energy ratio and the amount of floating of the head, and the abscissa is the peripheral speed of the disk. From FIG. 3, it will be seen that the peripheral speed of the disk is 40 m/sec at the steady state as compared with the 10 m/sec at the time the head 7 starts to float away from the disk 3. The sliding energy ratio at 40 m/sec is 16 times as large as that at 10 m/sec. Thus, at the steady state, the disk is scraped, upon collision, with such large sliding energy as mentioned and soon the recorded information is destroyed.
The magnetic disk storage unit is used for the main file in a computer system, and therefore the destruction of the information recorded in the magnetic disk storage unit will lead to the breakdown of the system, or will cause the most important problem.